Ankle exoskeleton system and method for assisted mobility and rehabilitation

ABSTRACT

A powered exoskeleton is designed to provide assistance to a user, where the powered exoskeleton may have power-generating elements in one location and power-applying elements in another location, so that a user can easily wear the powered exoskeleton.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Application No.62/644,163 filed on Mar. 16, 2018, the entire contents of which isincorporated herein by reference.

BACKGROUND

A number of injuries or conditions can lead to disorders, such ascerebral palsy (CP), that affect muscle control. Individuals with musclecontrol disorders such as CP frequently experience a downward trend ofreduced physical activity and worsening of gait function leading to apermanent decline in ambulatory ability. FIG. 1, for example, depicts asequence of events that can ultimately lead to loss of ambulatoryability. Specifically, in some individuals, diminished anklefunctionality results from lack of muscle strength, can lead to elevatedenergy costs associated with transport that, in turn, leads to reducedphysical activities. The reduced physical activities lead, in turn, tosecondary health issue, muscle weakness, and reduced gait functionleading to loss of ambulatory function. FIG. 2A is a chart depictingtypical reductions in steps taken for individuals having muscle controldisorders as compared to individuals without muscle control disorders.For children with CP, for example, walking can be drastically moreenergetically expensive than for their typically developing peers.Muscle strength and endurance do not increase in proportion to body massduring growth, factors contributing to declining walking ability. Theability to walk is critical for physical health and general well-beingacross the life-span. Reduced level of weight-bearing physical activitycontributes to a wide range of secondary conditions associated with CP,such as metabolic dysfunction, cardiovascular disease, fatigue,weakness, osteoporosis, and chronic pain.

By improving walking economy, individuals with CP may engage in greateramounts of habitual physical activity. This may prolong walking abilityand have many additional physical and mental health benefits, such asincreasing muscle and bone mass. Additionally, increased daily activitywould likely also have rehabilitation related benefits, includingmaintenance or improvement of baseline walking ability, by increasingmuscle strength and coordination.

A powered exoskeleton is a wearable, mobile device that allows a user toperform limb motions with additional external power, for increasing auser's strength or endurance. Powered exoskeleton usage may includerehabilitation, assistance, and enhancement of a user's capabilities.

SUMMARY

The above features and advantages of the present invention will bebetter understood from the following detailed description taken inconjunction with the accompanying drawings.

In accordance with an embodiment, a wearable assistance device mayinclude a battery, a motor, a cable, a first arm, a second arm, arotational bearing, a sensor, and a controller. The motor may beelectrically coupled to the battery. The cable may be coupled to themotor at a first end of the cable. The first arm may be configured toremovably couple to a lower leg of a user. The second arm may be coupledto a second end of the cable, and the second arm may be configured to bepositioned underneath a foot of the user. The rotational bearing mayrotationally couple the first arm to the second arm. The sensor may becoupled to the rotational bearing or the second arm, and the sensor maybe configured to measure a torque applied to the sensor or a pressureapplied to the sensor. The controller may be electrically coupled to themotor. The controller may be configured to receive data from the sensor,to determine a current state value using the data from the sensor, todetermine a control instruction based at least on the current statevalue, and to control an operation of the motor based on the controlinstruction.

In accordance with an example embodiment, a system may include a motor,a force-transmitting linkage, a lower assembly, a controller, and asensor. The force-transmitting linkage may be mechanically coupled tothe motor. The lower assembly may include a joint mechanically coupledto the force-transmitting linkage, and the lower assembly may beconfigured to engage a foot of a user. The controller may becommunicably coupled to the motor, and the controller may be configuredto transmit an instruction to the motor. The sensor may be coupled tothe lower assembly and communicably coupled to the controller, and thesensor may be configured to detect motion or force of the joint. Thecontroller may be configured to receive data from the sensor, and thecontroller may be configured to use the data to determine theinstruction to be transmitted to the motor.

In accordance with an example embodiment, a method of providingassistance to a user may include receiving data from a sensor coupled toa lower assembly, with the lower assembly including a joint mechanicallycoupled to a force-transmitting linkage and with the lower assemblybeing configured to engage a foot of a user, determining an instructionbased on the data from the sensor, and controlling an operation of amotor coupled to the force-transmitting linkage based upon theinstruction.

DESCRIPTION OF THE DRAWINGS

The drawings described herein constitute part of this specification andincludes exemplary embodiments of the present invention which may beembodied in various forms. It is to be understood that in someinstances, various aspects of the invention may be shown exaggerated orenlarged to facilitate an understanding of the invention. Therefore,drawings may not be to scale.

FIG. 1 depicts a diagram of the natural progression of ambulatorydecline in individuals with cerebral palsy (CP) that occurs in a largeportion of the population.

FIG. 2A shows statistically significant differences in daily total stepcount by CP functional level.

FIG. 2B shows the relationship between the oxygen cost and physicalactivity level.

FIG. 2C shows the ankle joint power across gait cycle during barefoot,hinged ankle-foot orthose (h-AFO), and dynamic ankle-foot orthose(d-AFO) walking in a child with CP compared to normal power profile.

FIG. 3 is schematic of an embodiment of an ankle-foot orthosis (AFO)exoskeleton.

FIG. 4 is a front view of an upper assembly of the AFO.

FIG. 5 is a rear view of the upper assembly of the AFO depicted in FIG.4.

FIG. 6 is a side view of a lower assembly of the AFO.

FIG. 7A depicts aspects in a gait cycle of an individual, withcorresponding sensor readings.

FIG. 7B depicts desired torque output, corresponding to the gait cycleof FIG. 7A.

FIG. 7C depicts feedback control of torque output.

FIG. 8 is a schematic of the exoskeleton control design to addressequinus deformity resulting in “tip-toe” gait.

FIG. 9 is a schematic depicting the operation of a balance-assistingexoskeleton (left) and a real-time control framework (right).

FIG. 10 is a table of torque values generated by the AFO and a user.

FIG. 11A depicts schematics of a timing of a powered ankleplantar-flexor assistance during walking.

FIG. 11B depicts schematics of a timing of a powered ankleplantar-flexor assistance during stair ascent.

DETAILED DESCRIPTION

The present system and method employs the use of powered assistance(e.g. ankle assistance) designed to increase or facilitate mobility in auser (e.g. in children or individual with muscle disorders such as CP).Wearable exoskeletons that may be used during daily life may offer atransformative new option for improving mobility by reducing barriers tophysical activity, such as for individuals with neurologically-basedgait disorders. Challenges to mobility faced by individuals (e.g.individuals with gait deficits from CP) may include prohibitively highmetabolic cost of transport, and difficulty completing strength- andbalance-intensive weight-bearing tasks such as navigating stairs andaround or over obstacles. For improving gait mechanics and walkingefficiency, robotic joint (e.g. ankle) actuation can provide positivepower to the body through appropriately-timed assistance (e.g.plantar-flexion assistance).

Wearable exoskeletons offer a unique alternative to existing assistancemethods e.g. for pediatric gait disorders caused by CP. As one example,an approach suitable for ambulatory children with CP may provide burstsof assistive torque at specific intervals throughout the gait cycle todynamically improve posture and retrain the neuromuscular system byencouraging volitional muscle activity. This type of powered assistancemay seek to maintain and ultimately augment the wearer's range of motionand muscle strength. Furthermore, by offering the potential todrastically reduce the metabolic cost of activity (e.g. walking),powered joint (e.g. ankle) assistance may lead to increases in habitualphysical activity.

As a particular example, the ankle joint plays a critical role inwhole-body stability and forward propulsion during walking. Dynamicankle actuation and stability control are required for independent andeffective function at home and in the community. Assistance at or nearthe ankle joint appears to provide significant improvement in walkingeconomy and has the potential to reduce the metabolic cost of transport.

In an embodiment, for improving gait mechanics and walking efficiency,robotic actuation (e.g. ankle actuation) can provide positive power tothe body through appropriately-timed assistance (e.g. plantar-flexionassistance) during the walking process. For improving performance duringbalance-intensive tasks, an exoskeleton (e.g. an ankle exoskeleton) canrespond rapidly to perturbations or abrupt changes in posture bymodulating joint torque, and therefore joint impedance, in real-time.

An embodiment may apply force to assist a user. This force may be linearforce or may be rotational force (i.e. torque). A torque is a specifickind of force, applied around a rotational axis.

In an embodiment, the present exoskeleton may provide dynamic “bursts”of assistance, as compared to existing rehabilitation-orientedexoskeletons, which operate by slowly repositioning each limb alongdesired joint trajectories. Specifically, in the present devicemotorized assistance may be provided by a powered ankle-foot orthosis(AFO). An embodiment of the present AFO 98 is shown in FIGS. 3-6.Specifically, FIG. 3 depicts a perspective view of AFO 98. FIG. 4depicts a front perspective view of upper assembly 100 of AFO 98, whileFIG. 5 depicts a rear perspective view of upper assembly 100 of AFO 98.FIG. 6 depicts a side view of lower assembly 104 of AFO 98. Takentogether, AFO 98 comprises an upper assembly 100, a transmissionassembly 102, and a lower assembly 104. Specifically, AFO 98 includestwo lower assemblies 104 for a right foot and a left foot of a user. Thepresent description describes the operation of a single lower assembly104, though it should be understood that a second lower assembly 104 mayhave a similar configuration and be operated according to the algorithmsdescribed herein in association with the user's other foot. The upperassembly 100 comprises attachment straps 106 used to attach the upperassembly 100 to a user (e.g. at a user's waist). The attachment straps106 may alternately be of a waist strap form, a backpack form, or anyother means of supporting weight on the user's waist, torso, or otherattachment site.

The attachment straps 106 may be coupled, directly or indirectly, to amotor base plate 108. The motor base plate 108 may provide a rigidsurface for mounting or supporting components of the upper assembly 100.The upper assembly 100 may additionally comprise a housing shell 110,which may serve to cover or protect internal components of the upperassembly 100 from direct view or interference. The housing shell 110 maycomprise any covering material (e.g. plastic, aluminum, cloth) suitablyarranged to cover the upper assembly 100. In an alternate embodiment,the motor base plate 108 and the housing shell 110 may be embodied as asingle component, which may comprise a single piece or multiple pieces.The motor base plate 108 may be coupled to the housing shell 110 bymeans of a plate-to-housing attachment 112. This plate-to-housingattachment 112 may comprise removable fasteners, with examples includingbolts, magnets, clips, and slots.

Additional components of the upper assembly 100 are shown in FIG. 4, ina front three-quarter or perspective view. This view is shown withoutthe attachment straps 106, the motor base plate 108, and the housingshell 110, which have been hidden in this figure to reveal underlyingcomponents. The upper assembly may comprise one or more force-generatingmotors 114. This one or more motors may comprise any means to generateforce, with examples including rotary electric motors, linear electricmotors, hydraulic pistons, pneumatic pistons, and pneumatic bladders.

The one or more motors 114 may be coupled to the motor base plate 108(see FIG. 3) by means of one or more motor brackets 116. The one or moremotor brackets 116 may be comprised of metal, plastic, or any othersuitable material for securing the one or more motors 114 to base plate108. The one or more motor brackets 116 may attach to the motor baseplate 108, the one or more motors 114, and to a motor top plate 122, bymeans of bolts, clips, slots, or other removable or non-removablefasteners.

The motor top plate 122 may provide a rigid surface for mounting orsupporting components of the upper assembly 100. The upper assembly mayfurther comprise motor electrical wiring 118, which may be coupled tothe one or more motors 114. The motor electrical wiring may be comprisedof one or more wires suited for carrying electrical power or electricalcontrol signals to and from the one or more motors 114, with an exampleembodiment comprising multiple strands of insulated copper wire. Themotor electrical wiring may be additionally coupled to one or morecircuit boards 120. The one or more circuit boards may comprise one ormore printed circuit boards (PCBs), mounting one or more circuits orchips, for performing one or more functions described in followingsections.

The one or more circuit boards 120 may be coupled to the motor top plate122, by means of bolts, clips, slots, or other removable ornon-removable fasteners. In an alternate embodiment, the one or morecircuit boards 120 may be coupled to one or more other components withinthe upper assembly 100.

The one or more motors 114 are additionally coupled to one or more motorpulleys 124. In an example embodiment, the one or more motor pulleys maycomprise double-wrap side-hole pulleys. In an alternate embodiment, theone or more motor pulleys may comprise any suitable means oftransferring force from the one or more motors 114 to one or moretransmission elements (e.g. one or more plantarflexion cables 126 andone or more dorsiflexion cables 128). Example alternate embodiments ofthe one or more motor pulleys 124 include cams, linear shafts, pistons,universal joints, and other force-transferring linkages.

The force generated by the one or more motors 114 is carried by one ormore transmission elements. In an example embodiment, the transmissionelements include one or more plantarflexion cables 126 and one or moredorsiflexion cables 128. The plantarflexion cables 126 and dorsiflexioncables 128 may be arranged to transfer opposing forces. Such anembodiment may arise due to the suitability of cables for transferring“pulling” forces but not for transferring “pushing” forces. In analternate embodiment, one or more single transmission elements may beused to transfer opposing (both pushing and pulling) forces. Theplantarflexion cables 126 and dorsiflexion cables 128 may be Bowdencables that transfer force via the movement of inner cables relative toa hollow sheath or housing containing the inner cable. Theplantarflexion cables 126 and dorsiflexion cables 128 may be comprisedof any suitable material, with examples including metal, Kevlar, andnylon.

The one or more plantarflexion cables 126 and one or more dorsiflexioncables 128 may each be housed in a cable sheath 130. The one or morecable sheaths 130 may serve to support and house the plantarflexioncables 126 and dorsiflexion cables 128. The one or more cable sheathsmay each be additionally coupled to barrel adjustors 132. The barreladjustors 132 may provide means for fine adjustment of the length of thesheaths 130, and thereby provide means for adjustment of the baselinetension of the plantarflexion cables 126 or dorsiflexion cables 128, aswell as adjustments of the plantarflexion cables 126 and dorsiflexioncables 128 for purposes of fitting or adjusting AFO 98 to differentusers. The one or more barrel adjustors may be further coupled to one ormore cable brackets 134, for purposes of support. The one or more cablebrackets 134 may be further coupled to one or more of the motor topplate 122, the motor base plate 108, or any other rigid element of theupper assembly 100.

The upper assembly 100 is shown in FIG. 5 in a rear three-quarter view.This view is shown without the housing shell 110, to reveal underlyingcomponents. The upper assembly 100 may additionally comprise one or morebatteries 136. The one or more batteries may be coupled to the motor topplate 122, or to the circuit board 120, or to any rigid component of theupper assembly 100, by removable or non-removable attachments (e.g.brackets or bolts). The one or more batteries 136 may comprise anysuitable means for storing and delivering electrical power, withexamples including nickel cadmium, nickel metal hydride, lithium ion,lead acid, alkaline, and lithium batteries. The one or more batteries136 may be rechargeable or single use. The upper unit 100 may furthercomprise circuitry and components for connecting and rectifying externalelectrical power received from external sources to provide means forcharging of a rechargeable embodiment of the one or more batteries 136.

Returning to FIG. 3, the one or more plantarflexion cables 126,dorsiflexion cables 128, and cable sheaths 130 may be routed down one ormore legs of a user to reach the lower assembly 104. This collection ofcables and sheathings comprises a transmission assembly 102. Thetransmission assembly 102 may alternately be any means of transferringforce from the upper assembly 100 to the lower assembly 104. In apreferred embodiment, the transmission assembly 102 is substantiallylightweight and substantially flexible so as to allow minimal impedimentof motion of the knee and hip joints of a user. The AFO 98 may includeone or more lubricating fluids or materials, disposed on an element orbetween two relatively-moving elements to reduce friction and increaseefficiency. Example locations of lubrication may include: insidebearings 152; inside motors 114; and between cables (e.g. plantarflexioncable 126 or dorsiflexion cable 128) and their respective sheaths 130.

The lower assembly 104 of AFO 98 is shown in FIG. 6 in a side view. Thelower assembly 104 may configured to attach to a foot 160. It will beapparent to a person of ordinary skill in the art that two lowerassemblies 104 may be used to couple to each foot of a user of AFO 98.The cable sheaths 130 of the transmission assembly 102 may be coupled tothe lower assembly 104 by lower barrel adjusters 138. The lower barreladjustors 138 may provide means for fine adjustment of the length of thesheaths 130, and thereby provide means for adjustment of the baselinetension of the plantarflexion cables 126 or dorsiflexion cables 128housed within the sheaths 130 and also adjusting the plantarflexioncables 126 and dorsiflexion cables 128 to fit the wearer of lowerassembly 104. The one or more barrel adjustors 138 may be mounted on asupport block 140. The one or more support blocks 140 may each beadditionally coupled to an upright 142. The one or more uprights 142 mayserve as a mounting or support element for the components of the lowerassembly 104.

After passing through the barrel adjusters 138 and exiting their sheaths130, the one or more plantarflexion cables 126 and one or moredorsiflexion cables 128 may couple to one or more sprockets 144. Thesprocket 144 may clamp to each of an opposing pair of one plantarflexioncables 126 and one dorsiflexion cables 128, wherein an opposing pair maycomprise two cables coupled to a single motor pulley 124 in the upperassembly 100. In an alternate embodiment, an opposing pair may insteadembodied in a single element with the capability to transfer bothpositive and negative forces. In an alternate embodiment, the sprocket144 may comprise any means for capturing force from a transmissionassembly 102 to produce torque between two or more attachment pointswith at least one attachment point on each of the distal side and theproximal side of the user's ankle joint (e.g., torque between the insolebracket 156 and the orthotic cuff 146).

Each upright 142 may be additionally coupled to an orthotic cuff 146,which is most readily visible in FIG. 3. The orthotic cuff 146 may beadditionally coupled to a D-ring strap 148 and a Velcro strap 150. Theorthotic cuff 146, D-ring strap 148, and Velcro strap 150 may beconsidered together as an attachment mechanism for coupling the lowerassembly 104 to a leg of a user at an attachment site which may beproximal to the ankle and distal to the knee of the leg of the user.

Each upright 142 may be additionally coupled to a bearing or joint 152.The one or more bearings 152 may each be additionally coupled to asprocket 144. Each of the one or more bearings 152 may serve as afreely-rotating and load-bearing connection between an upright 142 and asprocket 144. Each collection of an upright 142, a sprocket 144, and abearing 152 may be coupled by means of bolts and nuts or other suitableconnecting hardware.

The one or more sprockets 144 may each be additionally coupled to atorque sensor 154. The one or more torque sensors 154 may be used tosense the torque force applied by the exosketon to the user's anklejoint. Each torque sensor 154 may be additionally coupled to an insolebracket 156. The one or more insole brackets 156 provide means fortorque to be applied to a walking surface. The one or more insolebrackets 156 may be comprised of plastic, metal, or any suitable rigidmaterial. The one or more insole brackets 156 may be configured to beinserted into a user's footwear, by means of using thin elements withoutexternal straps.

Each upright 142 and insole bracket 156, taken in combination, may beconsidered as a force-applying arm forming a joint, where the twoforce-applying arms apply torque around an axis, where the axis isaligned with a body joint axis (e.g. an ankle joint axis). When a forceis applied along a length of plantarflexion cables 126 or dorsiflexioncables 128, that force is applied to sprocket 144 and, in turn, insolebracket 156. Accordingly, the forces applied along the lengths ofplantarflexion cables 126 and dorsiflexion cables 128 apply a forcecausing insole bracket 156 to rotate about bearing 152 with respect toupright 142.

In an alternate embodiment, the one or more sprockets 144 may be coupleddirectly to the corresponding one or more insole brackets 156 without anintermediate torque sensor 154.

In an embodiment, one or more accelerometers may be coupled the lowerassembly 104 to provide information on the user's gait.

The AFO 98 may be additionally coupled to one or more pressure sensors158. The one or more pressure sensors 158 may be comprised offorce-sensitive resistors, piezoresistors, piezoelectrics, capacitivepressure sensors, optical pressure sensors, resonant pressure sensors,or other means of sensing pressure, force, or motion. The one or morepressure sensors 158 may be arranged across the bottom area of theinsole bracket 156 to provide spatial pressure information across thefoot surface.

Referring back to FIG. 5, the one or more circuit boards 120 of AFO 98may comprise one or more of each of the following components orcontrollers: microprocessor circuitry (e.g. an ARM-basedmicroprocessor), power management circuitry, signal processingcircuitry, and motor driver circuitry. Each motor driver circuitry maybe additionally coupled to one or more motor wirings 118. Each powermanagement circuitry may be additionally coupled to one or morebatteries 136. Each signal processing circuitry may be additionallycoupled to one or more of: torque sensors 154 and pressure sensors 158,and any other sensors, such as accelerometers mounted on or coupled tocomponents of AFO 98.

In an embodiment, a controller circuitry coupled to the one or morecircuit boards 120 may operate a finite state machine to control theoperation of AFO 98 and, specifically, motors 114 to provide assistanceto a wearer for AFO 98. Specifically, the state machine implemented bythe controller may define a number of different states, including earlystance, late stance, and swing phases of the user's gait or step cyclethat, in turn, control which of motors 114 is operated to apply force toeither plantarflexion cables 126 or dorsiflexion cables 128 to provideforce assistance at the ankle of the wearer. Specifically, withreference to FIG. 6, when a pulling force is applied to plantarflexioncables 126 by motors 114, a torque force is applied to sprocket 144causing insole bracket 156 to be rotated downwards with respect toupright 142 thereby assisting the using in moving their toes downwards(i.e., plantarflexion). Conversely, when a pulling force is applied todorsiflexion cables 128 by motors 114, a torque force is applied tosprocket 144 causing insole bracket 156 to be rotated upwards withrespect to upright 142 thereby assisting the using in moving their toesupwards (i.e., dorsiflexion). In this manner, upright 142 and insolebracket 156 operate as first and second arms of a hinged connection atthe user's ankle. The first arm of the hinge (e.g., upright 142) isfixed to the user's ankle (e.g. by orthotic cuff 146 around the lowerleg), while the second arm of the hinge (e.g., insole bracket 156) ispositioned along a user's foot.

The state machine may receive input from one or more sensors (e.g. 154,158), and use current and previous input values in order to determine acurrent state of the state machine. The current state is then used todetermine the timing of the motor 114 activation, in order to providetorque assistance to the user with appropriate timing and intensity(e.g., to provide plantarflexion assistance during toe-off, ordorsiflexion assistance during foot swing to prevent drop foot).

To illustrate the stages of the state machine implemented by thecontroller of AFO 98, FIGS. 7A and 7B depict aspects of a gait cycle,the corresponding sensor 158 signals, and the corresponding outputforces.

Specifically, FIG. 7A shows a diagram 800 of a foot and AFO 98 positionthrough a gait cycle (top), along with corresponding readings fromsensors (bottom). In this example, the AFO 98 uses two pressure sensors158 on a foot: one proximal to the heel and one proximal to thefore-foot (e.g. under the ball of the foot). The readings from thesensors determine the state of the state machine. FIG. 7A depictsexample gait cycle states 810, 812, and 814, which correspond todifferent states in the state machine of the controller of AFO 98.Sensor readings 820, 822, and 824 show the readings from the sensors158. These readings 820, 822, 824 each instruct the state machine totransition to a corresponding state. These states may correspond to gaitphases such as “heel strike”, “toe off” and “swing”. For each state, thestate machine has output values. The state machine output at leastpartially determines the instructions to be delivered to the motor. FIG.7B shows an example of assistance output relative to gait cycle, whereinthe assistance output 802 is “on” (e.g. the assistive torque isnon-zero) during the times when the user's forefoot is applying pressureto the ground and assistive torque may be desired.

In an example embodiment, signals generated by a torque sensor 154mounted proximate the wearer's ankle may be used as input to a controlalgorithm (e.g. proportional-integral-derivative (PID) control) executedby the controller of the one or more circuit boards 120. The controlalgorithm may be used to ensure that the actual torque produced at theankle is substantially equivalent to the specified (i.e., desired)torque required while the wearer of AFO 98 walks. FIG. 7C shows anexample of a desired torque profile over time (dashed line 804) and ameasured torque profile (gray line 806). Feedback through a controlalgorithm may be used by one or more motor driver circuits to controlone or more motors 114.

As the user's foot proceeds through the gait cycle depicted in FIG. 7A,the pressure measurements captured by pressure sensors 158 will vary.Specifically, in an initial state at the beginning of the gait cycle(e.g., gait cycle state 810) when the user's toe first contacts a groundsurface, the pressure measured by a fore-foot pressure sensor 158 maybegin transitioning from a low or minimal value to a relatively high ormaximum value. After the user steps upon the ground 810, the user beginstransitioning through gait cycle state 812 as the measured fore-footpressure value gradually increases until it reaches a maximum. At thegait cycle state 814, the user's foot leaves the ground and the gaitcycle enters the swing phase. During the gait cycle, the controllermonitors the measured torque value and compares the measured torquevalue to the desired torque value to determine the instructions to bedelivered to the motors 114.

The controller may continue to operate in the on state (i.e., providingassistance) until the measurements of fore-foot and/or heel pressuresensors 158 fall below a threshold value. At that time, the controllermay determine that the gait cycle has entered a state in which theuser's foot has left the ground (e.g., state 814) and the controller cantransition, as illustrated in FIG. 7B to an off state.

While in the on state, the controller operates motors 114 to providephysical assistance to the user of AFO 98. Specifically, the controllertransmits control instructions to motors 114 to rotate in a directioncausing motors 114 to apply a pulling force against plantarflexioncables 126. This action causes a rotation force to be applied to insolebracket 156 in the same direction as the torque being applied by theuser. Accordingly, the controller operates motors 114 to provide anassistive force that compliments that already being provided by theuser.

During the on state, the forces applied by motors 114 are controlledbased upon instructions provided to the motors 114 by the controller. Inan embodiment, the controller controls the force applied by motors 114based upon the torque measurements gathered by torque sensors 154. Forexample, during the on state, the controller may cause the motors 114 toapply a rotational force to insole bracket that is a sufficient toachieve a specific value of the torque measured by torque sensor 154. Atarget torque value may be determined for each state in the gait cycle.The controller may then be configured to provide torque through theoperation of motors 114 that causes the applied torque measured bytorque sensor 154 and provided by the operation of motors 114 to reachto desired torque value (e.g. by a proportional-integral-derivative(PID) control scheme). Different desired torque values may be definedfor each states in the gait cycle.

During the off state, controller may be configured to be inactive by notoperating motors 114, thereby enabling free movement of insole bracket156. In some embodiments, however, the controller may be configured to,during the off state, operate motors 114 in a reverse direction (causinga pulling force to be applied to dorsiflexion cables 128) to assist theuser in raising the toes of the foot while the gait cycle is in theswing phase (e.g., state 814 of FIG. 7A).

Alternate embodiments may use other sensing modalities (e.g.accelerometers, torque sensors) to determine the gait cycle state (e.g.810, 812, 814) and thereby determine the timing of the AFO 98 assistiveoutput.

As shown in FIG. 7A, a state machine may operate by first comparing eachsensor reading (e.g. heel pressure and fore-foot pressure, from pressuresensors 158) to a threshold. If a reading is above a threshold, thestate machine may interpret the reading as a value of “on”; if thereading is below the threshold, the state machine may interpret thereading as a value of “off”. Then, if a heel pressure input is “on” anda fore-foot pressure input is “off”, the state machine may instruct thecontroller to set the desired torque output to zero. Then, if thefore-foot pressure input switches to “on”, then the state machine mayinstruct the controller to set the desired torque output to be anon-zero plantarflexion torque assistance output. This torque output mayincrease over time (as in FIG. 7B). Then, if the fore-foot pressurereading switches to “off”, the state machine may instruct the statemachine may instruct the controller to set the desired torque output tozero, or may instruct the controller to set the desired torque output tobe a non-zero dorsiflexion torque assistance output.

An example embodiment may additionally be configured to perform standingassistance. As shown in FIG. 9, standing assistance may be performed byusing sensors 504 (e.g. accelerometers, inertial measurement units) todetermine the user's balance 500 and posture 502, processing the sensorsignals according to control algorithms on the circuit boards 120 todetermine a desired torque 506, and controlling the motors 114 to applytorque 508 to the ankle to configured to assist a user in maintainingbalance 500.

For example, based upon sensor data (e.g. captured from torque sensor154 pressure sensors 158, accelerometers, inertial measurement units),the controller may determine that the user of AFO 98 is not walking andis instead standing still. If the user is standing still, the operationof the controller may be modified. Instead of providing an assistiveforce (as in the mode of operation described above in conjunction withFIGS. 7A-7C), the controller may provide an opposing force to that beingmeasured an accelerometer sensor. Specifically, as the user is standingstill, the controller may operate motors 114 in an attempt to stabilizean accelerometer reading, thereby assisting the user to stand still inan upright position.

Accordingly, if an accelerometer sensor measures an excessive leaningangle in a first direction, the controller may operate motors 114 topull on one of plantarflexion cable 126 or dorsiflexion cable 128 sothat an opposing torque force is generated, thereby returning theleaning angle to below excessive values. Such operation may assist theuser in standing upright with relatively little ankle motion.

In an example embodiment, an exoskeleton may be customized for eachindividual user. Customization may include adjusting the size or shapeof one or more components to fit a user. Example adjustments includesettings for: the length of the one or more dorsiflexion cables 128,plantarflexion cables 126, and their respective sheaths 130; the sizeand shape of the one or more insole brackets 156; the length and shapeof the one or more uprights 142, the size and shape of the one or moreorthotic cuffs 146, and the length and arrangement of the attachmentstraps 106.

In an embodiment, the amount of assistance provided to a user's anklejoints may be further customized based on restoring positive power tonormal levels. Table 1300 shown in FIG. 10 shows an example of theamounts of torque and power produced by the user's ankle, by the AFOexoskeleton, and by the combined user+AFO 98. In an example, the torqueand power produced by the combined user+AFO 98 may be substantiallyequivalent to a target torque and power. The target torque and power maybe designed to be equivalent to that of an individual having a typical(non-CP) gait and having age and/or body mass substantially equivalentto that of the AFO 98 user. This embodiment is further shown in FIG. 11Awith diagrams showing leg position 400 and ankle power 402 duringwalking, and in FIG. 11B with diagrams showing leg position 404 andankle power 406 during stair climbing.

The preceding example embodiments do not distinguish between “left” and“right” components of the exoskeleton. In an example embodiment, asdepicted in FIG. 3, there may be a symmetrical arrangement of allcomponents in the transmission assembly and lower assembly such that theAFO may assist both the left leg and the right leg of the user. Theupper assembly need not be symmetric in this embodiment, except insofaras it is coupled to the transmission assembly.

In an example embodiment, the components having greatest mass (e.g.motors 114, batteries 136) may be placed near to the user's center ofmass (e.g. hips or torso). In such an example embodiment, thetransmission assembly 102 may serve to deliver torque to the lowerassembly 104 without placing undue weight on the distal elements of theuser's legs. Such an embodiment may serve to maximize walking economy,by minimizing the metabolic cost due to the mass added to the body.

In an example embodiment, the AFO 98 may be configured such that thetransmission assembly 102 is capable of at least partially supporting oroffloading the weight of the upper assembly 100, thereby transferringthe weight of the upper assembly directly to the lower assembly 104.This supporting or offloading function may be modulated by the gaitcycle of the user. As an example, a Bowden cable transmission assemblymay be aligned or otherwise configured such elements that thetransmission assembly 102 may push upwards on the upper assembly 100when the corresponding limb is on the ground, and elements of thetransmission assembly 102 may remain flexible when the correspondinglimb is in motion. In this manner, the offloading may reciprocatebetween two limbs as the limbs each transition between stance phase

and swing phase. An ability of a transmission assembly 102 to at leastpartially support an upper assembly 100 may reduce the overall metabolicburden on a user.

An alternate embodiment may comprise one or more chain componentsattached to one or more ends of one or more plantarflexion cables 126 ordorsiflexion cables 128. The one or more chain may be additionallycoupled to at least one of a sprocket 144 or a motor pulley 124. Such achain may serve as a flexible force-transferring linkage connecting asprocket 144 or pulley 124 to a plantarflexion cable 126 or dorsiflexioncable 128, and thereby would allow actuation of the cable (126 or 128)without requiring the cable to bend around the radius of the sprocket144 or motor pulley 124.

An embodiment may additionally comprise modular attachment points, whichmay be coupled to one or more insole brackets 156, sprockets 144, ortorque sensors 154, and which may be configured to mount to multiplevarious platforms (e.g. an individual's shoes, a custom molded orthoticinsert made from thermo-plastic).

An embodiment may be suited particularly for individuals with CP whodrag their toes excessively (e.g. due to prior usage of a passive AFO 98preventing plantar-flexion). Such an embodiment may be configured toapply force for dorsi-flexor assistance during the swing phase of theuser's gait.

An embodiment may be used to assist individuals having an equinusposture. In such an embodiment, an exoskeleton attachment may be used toprovide a “virtual ankle” actuation 700 in series with the biologicalankle joint. Such an embodiment may incorporate a cam mechanism 702configured to rotate under a raised heel to provide positive power (FIG.8).

An embodiment may facilitate lasting motor adaptation via plasticity ofthe neuromuscular system. Short-term motor adaptation may be prolongedvia repetitive training and reinforcement e.g. in individuals withneurological deficits; extended periods of motor training with externalassistance may guide the establishment of new, more permanent motorpatterns. This embodiment may be used to provide lasting rehabilitationoutcomes, e.g. in children with CP. Such an embodiment may entailrepeated use of the AFO 98 over a period of weeks or months, with such arepeated use occurring the context of rehabilitation or of everydayactivity. Such an embodiment may further entail adjustments of the AFO98 output in order to facilitate lasting motor adaptation (e.g. loweringthe AFO 98 output over time).

An embodiment may be additionally used to provide exercise or trainingto a user. In such an embodiment, the motor 114 control may beconfigured to apply resistance to one or more joints of the user duringmotion. An embodiment may be configured to sense motion of a user andapply torque to partially counteract the torque generated by the user.An embodiment may additionally comprise an “exercise switch”, allowing auser or other individual to switch between “exercise” and “assistance”settings, wherein the exercise mode AFO 98 is turned off and does notprovide force assistance to the wearer. An embodiment may additionallycomprise an interface, communicably connected to the one or more circuitboards 120, allowing a user or other individual to set or programdesired forces (e.g. motor 114 outputs or torque sensor 154 readings)for assistance or exercise.

An embodiment may additionally comprise a communication system,electrically connected to a circuit board 120 of an AFO 98. Such acommunication system may be configured to transmit and/or receiveinformation. Information that may be transmitted includes: user walkingtime, sensor reading logs, performance metrics, and other informationgenerated or sensed by the AFO 98. Information that may be receivedincludes: control software updates, training exercise settings,assistance settings, and other information that may modify the functionof the AFO 98. Such a communication system may allow for individualizedtraining and control of an AFO 98, specific for each user. Such acommunication system may communicate to a remote server “cloud”, or maycommunicate by other internet-based means, or may communicate to localdevices.

An embodiment may additionally comprise one or more “disengage switches”allowing a user or other individual to disconnect one or moreforce-transferring connections of an exoskeleton. An example of thisembodiment may comprise a removable force-transferring connection (e.g.a removable pin or a switchable clamp) connecting a sprocket 144 to atorque sensor 154 and insole bracket 156, or any other connectionbetween two rotating parts that may be toggled such that the rotatingparts are linked or unlinked. In an embodiment, disengaging aforce-transferring connection (e.g. removing a pin or loosening a clamp)may allow the insole bracket 156 and the sprocket 144 to rotateindependently. Disengaging a force-transferring connection in anembodiment may allow a user to walk, sit, or perform any other activitywithout assistance or interference from AFO 98.

The described features, advantages, and characteristics may be combinedin any suitable manner in one or more embodiments. One skilled in therelevant art will recognize that the circuit may be practiced withoutone or more of the specific features or advantages of a particularembodiment. In other instances, additional features and advantages maybe recognized in certain embodiments that may not be present in allembodiments.

Reference throughout this specification to “one embodiment,” “anembodiment,” or similar language means that a particular feature,structure, or characteristic described in connection with the embodimentis included in at least one embodiment. Thus appearances of the phrase“in one embodiment,” “in an embodiment,” and similar language throughoutthis specification may, but do not necessarily, all refer to the sameembodiment.

I claim:
 1. A device, comprising: a motor; a force-transmitting linkage,mechanically coupled to the motor, wherein the force transmittinglinkage comprises a first cable and a second cable coupled to the motorsuch that the motor applies tension to the first cable when rotating ina first direction and applies tension to the second cable when rotatingin a second direction; a lower assembly including a joint mechanicallycoupled to the first and second cables, such that the joint experiencestorque in a first direction upon application of tension to the firstcable and experiences torque in a second direction upon application oftension to the second cable, the lower assembly being configured toengage a foot of a user; a controller, communicably coupled to themotor, wherein the controller is configured to transmit an instructionto the motor; and a sensor coupled to the lower assembly andcommunicably coupled to the controller, wherein the sensor is configuredto detect motion or force of the joint; wherein the controller isconfigured to receive data from the sensor, and wherein the controlleris configured to use the data to determine the instruction to betransmitted to the motor wherein the force-transmitting linkage includesa Bowden cable, and wherein the Bowden cable is adapted to have a lengthwhich is substantially matched to a length of a leg of the user, suchthat when the leg is straight the Bowden cable is substantially straightbetween the lower assembly and the motor, and such that when the Bowdencable is straight the Bowden cable acts to partially support the weightof the device by providing resistance to compressive force between lowerassembly and the motor.
 2. The device of claim 1, wherein the jointincludes a first arm, a second arm, and a rotational bearing coupled tothe first arm and the second arm, the first arm is configured to becoupled to a lower leg by a cuff, and the second arm is configured to becoupled to a foot plate, a shoe, or a cam beneath the user's foot. 3.The device of claim 2, wherein the sensor is a pressure sensor, whichgenerates a pressure measurement value; and wherein, when the pressuremeasurement value is greater than a threshold pressure measurementvalue, the controller is configured to cause the motor to apply a forcealong a length of the force-transmitting linkage in a first direction.4. The device of claim 3, further comprising a second sensor, whereinthe second sensor is a torque sensor coupled to the rotational bearing,which generates a torque measurement value, and wherein an amount offorce applied by the motor along a length of the force-transmittinglinkage in a first direction is at least partially determined by thetorque measurement value.
 5. The device of claim 3, wherein, whenpressure measurement value less than the threshold pressure measurementvalue, the controller is configured to cause the motor to apply a forcealong the length of the force-transmitting linkage in a seconddirection.
 6. The device of claim 3, wherein, when the pressuremeasurement value less than the threshold pressure measurement value,the controller is configured to prevent the motor from applying forcealong a length of the cable.
 7. The device of claim 1, furthercomprising a disengagement mechanism configured to selectivelydisconnect the force-transmitting linkage from the lower assembly or themotor.
 8. The device of claim 1, further comprising a housing andwherein the motor is disposed within the housing and the housing isconfigured to be worn proximate a waist of the user.